Synthetic polymeric materials are widely used in a variety of applications. The environmental degradability of these polymeric materials has recently become important, primarily due to the concerns of limited landfill space and accumulation of liter. Synthetic polymers are in general not biodegradable. The carbon to carbon bonds in the backbone of most synthetic addition polymers are not very susceptible to biological cleavage and this makes these polymers generally quite resistant to biodegradation.
One possible method of solving this problem would be to blend degradable materials, such as starch, with synthetic polymers so that the structure, such as a film, is broken down and looses its structural integrity by the action of living organisms or light. However, when this happens, the actual synthetic polymer itself is not degraded but is simply in the environment in a particulate form. Thus, synthetic polymers that are themselves biodegradable and would disappear from the environment are very desirable.
Low melting, low molecular weight polyesters are known to be biodegradable. Synthetic addition polymers with an easily hydrolyzable group, such as an ester group, in the polymer chain are also known to be biodegradable. Copolymers of cyclic ketene acetals such as 2-methylene-1,3-dioxepane and ethylene are known see Bailey et. al., Makromol. Chem., Macromol Symp., Vol. 6, 81-100 (1986). These copolymers are prepared with ethylene in the presence of a peroxide initiator resulting in a copolymer containing ester groups in the backbone. Processes for producing these cyclic ketene acetals are known, however, these processes have low yield, low conversion, are time consuming and/or are expensive and in some instances produce unstable cyclic ketene acetals that decompose or polymerize spontaneously.
Cyclic ketene acetals are unstable compounds and in general lead to spontaneous polymerization. The tendency to polymerize increases as the purity of the product increases. Processes for purifying these cyclic ketene acetals are known, however, these processes do not prevent spontaneous polymerization and do not produce relatively pure cyclic ketene acetals and/or are time consuming and expensive.
McElavin, S. M. and Curry, J. M.; Journal American Chemical Society, Vol. 70,3781-3786 (1948) disclose the synthesis of 2-methylene-1,3-dioxolanes and 1,3-dioxanes by dehydrohalogenation of the corresponding halogenated cyclic acetals using potassium t-butoxide in t-butyl alcohol. The cyclic ketene acetals were obtained pure only with difficulty because the purer the acetal the more rapidly it polymerized.
U.S. Pat. No. 3,431,281 discloses 2-methylene-1,3-dioxolane which does not immediately polymerize. This compound is prepared by mixing 2-chloromethyl-1,3-dioxolane with a solution of liquid ammonia and a alkali metal such as sodium or potassium. It was disclosed that the monomer could be stored for at least 10 days.
Taskinen and Pentikainen, Tetrahedron, Vol. 34, 2365-2370 (1978) disclose the preparation Of 2-methylene-1,3-dioxepane and other cyclic ketene acetals by dehydrohalogenation of the chlorine derivatives with solid potassium t-butoxide. 2-methylene-1,3-dioxolane was not isolated as a pure compound (it polymerized immediately) but as a mixture with the other reaction product t-butanol. In many cases the ketene acetal was collected as a mixture with t-butanol. The alcohol could be removed from the mixture by azeotropic distillation with hexane, after which the pure ketene acetal could be collected unless it was too readily polymerizable to allow isolation in pure state.
Bailey et. al., J. Polymer Science (Poly. Chem. Ed. Vol. 20, 3021-3030(1982) disclose synthesis of 2-methylene-1,3-dioxepane by dehydrohalogenation of the corresponding chlorine derivative using potassium t-butoxide in t-butyl alcohol. Ether was added and the precipitate was removed by filtration. Solvents were removed by distillation and the crude product was vacuum distilled to give a product containing a trace of t-butanol. Further purification by distillation from metallic sodium produced 72 percent yield of 2-methylene-1,3-dioxepane, disclosed as being surprisingly stable. An alternative method for synthesizing 2-methylene-1,3-dioxepane using potassium hydroxide in I hexadecene with 2-chloromethyl-1,3-dioxepane was also disclosed. After 12 hours at 130.degree. C., the product was distilled from the mixture under partial vacuum to give a liquid, which was further purified by distillation over metallic sodium to give a yield of 66 percent.
EP 095,182 discloses the synthesis of several cyclic ketene acetals including 2-methylene-1,3-dioxepane using dehydrohalogenation of the halogen derivatives using potassium t-butoxide in t-butyl alcohol. The reaction took 8 hours at 100.degree. C. After 8 hours the mixture was extracted with ether. After removing the solvent, the residue was distilled under reduced pressure to obtain 72 percent yield of the product 2-methylene-1,3-dioxepane.
Fukuda et. al., Tetrahedron Letters, Vol. 27, No. 14, 1587-1590(1986) disclose the synthesis of cyclic ketene acetals using dehydrohalogenation of the chloro derivative by potassium t-butoxide in t-butyl alcohol. The isolation and purification steps were not reported.
Although the preparation and isolation of cyclic ketene acetals such as 2-methylene-1,3-dioxepane are known the above processes either produce unstable forms, are very slow and expensive, or have poor conversion and selectivity. It would, therefore, be desirable to be able to produce pure cyclic ketene acetals for the preparation of biodegradable synthetic polymers that are efficient and effective.